Electrolytic cells for preparing alkalis by the mercury process

ABSTRACT

In an electrolytic cell designed for use in the mercury process and provided with longitudinal side grooves closely adjacent the surface of sidewalls, auxiliary grooves are provided on the surface of the bottom plate in parallel with the sidewalls at positions 1 to 10 cm. spaced apart therefrom to minimize lateral movement of mercury.

United States Patent Inventor Teruo Imai Iwaki-shi, Japan Appl. No. 791,400 Filed Jan. 15, 1969 Patented Oct. 26, 1971 Assignee Kureha Kagaku Kogyo Kabushiki Kaisha Tokyo-To, Japan Priority Jan. 19, 1968 Japan 43/2672 ELECTROLYTIC CELLS FOR PREPARING ALKALIS BY THE MERCURY PROCESS Primary Examiner-John H. Mack Assistant Examiner-D. R. Valentine Attorneys-Ward McElhannon and Brooks & Fitzpatrick ABSTRACT: In an electrolytic cell designed for use in the mercury process and provided with longitudinal side grooves closely adjacent the surface of sidewalls, auxiliary grooves are provided on the surface of the bottom plate in parallel with the sidewalls at positions 1 to 10 cm. spaced apart therefrom to minimize lateral movement of mercury.

4 Claims, 2 Drawing Figs.

US. Cl 204/219, 204/250 Int. Cl C22d 1/04 Field of Search 204/219, 220, 250, 99

L] I III M PATENTEDnm 26 I871 3.616.430

FIG. I

FIG. 2

fLIj/I/ k I BACKGROUND OF THE INVENTION This invention relates to a novel electrolytic cell for preparing alkalis by the mercury process and more particularly to an improved construction of an iron bottom plate of the electrolytic cell.

It has been well known to provide narrow longitudinal grooves along sidewalls of the electrolytic cell for preparing alkalis by the mercury method or along both sides of an anode support upwardly projecting from the bottom plate for the purpose of making uniform the flow of mercury on the bottom plate.

The purpose of providing such longitudinal side grooves is as follows.

If the surface of the bottom plate were perfectly flat in the transverse direction in an electrolytic cell without any anode support projecting from the bottom plate, the mercury will flow as a lump owing to its extremely high surface tension and cohesive force, when one tries to cause the mercury to flow in the form ofa thin film, so that it is difficult to cause the mercury to flow in the form of a thin film of uniform thickness. Where longitudinal side grooves are provided on both side edges of the bottom plate, the streams of mercury which flow through these grooves attract the stream of mercury which flows at the central region of the bottom plate toward opposite side edges so that mercury can flow in the form of a thin film of uniform thickness. In an electrolytic cell having a longitudinal anode support along the longitudinal center line of the bottom plate, similar uniform flow of mercury can be assured by providing longitudinal side grooves on the opposite sides of the anode support. For the sake of brevity, longitudinal sidewalls and longitudinal anode support are hereinafter designated as longitudinal walls or longitudinalwall members.

Even in an electrolytic cell provided with such side grooves the bottom iron plate is often exposed at these grooves owing to fluctuations or lateral movements of the mercury streams. Since the surface of these longitudinal wall members is generally made of or lined with an electric insulator such as rubber, synthetic resin, ceramics and the like, and since an extremely high interface tension is produced between these insulating materials and mercury, the mercury has a tendency to be repelled away from the surface of the longitudinal wall members. Ordinarily, since mercury flows in a direction parallel to the surface of the longitudinal wall members, it is inevitable for the mercury to flow along a tortuous path or to form transverse waves on the surface of the mercury due to slight irregularity or inclination of the surface of the bottom plate, or due to the effect of nonunifonn flow of the electrolyte caused by such obstacles as the electrode immersed therein or bubbles caused by the evolution of chlorine gas. Tortuous flow of the stream of mercury or transverse waves on the surface of mercury act to assist repulsion between mercury and longitudinal wall members thus completely separating them to expose portions of the surface of iron at the bottom of side grooves. Then the electrolyte and contaminants such as so-called mercury butter essentially consisting of iron-mercury amalgam formed in the electrolytic cell enters into the gap between the mercury and longitudinal wall members. As the mercury butter has much smaller interface tension with respect to the insulating material than mercury, it will adhere to the wall members. When portions of the bottom plate are exposed or when the mercury butter adheres to the longitudinal wall members, hydrogen will be evolved at such portions thus causing a decrease in the current efficiency and corrosion of the bottom plate. Moreover, the electrolyte that has adhered to the lower portion of the longitudinal wall members reacts with mercury amalgam to evolve hydrogen. At the same time, the electrolyte is concentrated to precipitate crystals. Precipitated crystals of a salt absorb the electrolyte to act as nuclei. In this manner, crystals grow gradually to cause severe local corrosion of the bottom plate.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a novel electrolytic cell for manufacturing alkalis by the mercury process wherein mercury is caused to flow in the form of a continuous thin film of uniform thickness, thus eliminating various problems described above.

In accordance with this invention, in an electrolytic cell for use in the mercury process having a bottom plate with longitudinal grooves closely adjacent to longitudinal wall members which define a flow passage for mercury in the electrolytic chamber, there are provided on the surface of the bottom plate auxiliary grooves in parallel with the longitudinal wall members and spaced therefrom by a distance ranging from I to 10 cm. preferably 2 to 5 cm. for preventing fluctuations or lateral movements of mercury.

BRIEF DESCRIPTION OF THE DRAWING This invention can be more fully understood from the following description taken in conjunction with the accompanying drawing in which:

FIG. I is a top plan view of an electrolytic cell embodying this invention and FIG. 2 shows an enlarged sectional view of the electrolytic cell taken along a line II-II in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT An electrolytic cell I shown in the accompanying drawing comprises an electrolytic chamber ll defined by longitudinal vertical sidewalls 3, end walls 12, an iron bottom plate 2 and one or more longitudinal anode supports 4. The inner surface of side end walls 3 and 12 are lined with rubber or other suitable insulating material 3a. Anode supports 4 are also made of I suitable insulating material such as fluorinated resin. Longitu dinai side grooves 5 and 6 are provided on the upper surface of bottom plate 2 closely adjacent to the surface of sidewalls 3 and anode supports 4. In the conventional electrolytic cell having a construction as above described, mercury supplied to a groove 9 on the inlet side flows through parallel passages defined by sidewalls 3 and anode supports 4 or longitudinal wall members and is discharged out of the cell through a duct 10 on the discharge side. According to this example, auxiliary longitudinal grooves 7 and 8 are provided on the surface of the bottom plate respectively in parallel with grooves 5 and 6 but properly spaced apart therefrom. In the illustrated example, auxiliary grooves 7 and 8 are spaced apart about 3 cm. from the surfaces of sidewalls 3 and electrode supports 4, respectively.

In the conventional electrolytic cell without auxiliary grooves 7 and 8, when mercury 11 flows in the transverse direction or when transverse waves are created on the surface of mercury, mercury comes to engage the surface of the longitudinal wall members and then reflected back to the opposite surface. As a result of such repeated reflections from opposing surfaces of the longitudinal wall members mercury flows along tortuous paths. In some cases, mercury will be perfectly separated from longitudinal wall members so as to locally expose portions of the bottom plate. In accordance with this invention, however, as the depth of mercury stream is deeper in auxiliary grooves 7 and 8 lateral movement of mercury is difficult in these grooves. Most of lateral movements or waves created in regions between auxiliary grooves 7 and 8 are stopped by these grooves so that their influence upon por tions of mercury closely adjacent longitudinal wall members can be precluded. For this reason, exposure of portions of the bottom plate near longitudinal wall members, deposition of the electrolyte or contaminant such as mercury butter on the surface of the longitudinal wall members and decrease in current efficiency as well as corrosion of the bottom plate caused thereby can be positively precluded.

The depth of the longitudinal auxiliary grooves may be from I to 5 mm. Depth of more than 5 mm. does not result in any additional merit and is rather uneconomical. The width of these auxiliary grooves may be 1 to 3 cm., preferably 2 cm., for example. The cross-sectional configuration of the auxiliary grooves may be triangular, as shown in FIG. 2, or semicircular. It is important to locate auxiliary side grooves. near side grooves which are located at the bottom of longitudinal wall members. It was determined that the distance between an auxiliary groove and an associated longitudinal wall member should be in a range of from 1 to cm., preferably from 2 to 5 cm. in order to prevent lateral movement of mercury. The applicant is aware of the fact that, in an electrolytic cell having a wide mercury passage, a longitudinal groove has been formed at the center of the passage. However, such a longitudinal groove is ordinarily spaced more than 20 cm. from the longitudinal wall members so that it can not effectively prevent lateral movement of mercury, because such lateral movement is the largest near the longitudinal wall members. Thus, the auxiliary grooves operate most effectively when they are located in the specified range near the longitudinal wall members.

Although in the electrolytic cell shown in the drawing mercury is admitted into and discharged from the cell through transverse grooves 9 and I0, it is to be understood that this invention is not limited to this particular type of electrolytic cell but that it may be applied to any horizontal type ofelectrolytic cell for preparing alkalis by the mercury method. For example, the anode support may be eliminated from the bottom plate or it is not necessary to be a continuous member, that is, it may be discontinuous. Moreover, the longitudinal wall members may not necessarily be made of an electric insulator such as rubber, fluorinated resin and the like, but instead the lower portion of the longitudinal wall members which are immersed in mercury may be made of iron.

I claim:

1. In an electrolytic cell for preparing alkalis by the mercury process comprising sidewalls, end walls and a bottom plate which cooperate to define an electrolytic chamber, means to cause mercury to flow, normally in the form of a thin layer, on the surface of said bottom plate and longitudinal side grooves provided on the surface of said bottom plate, said grooves being located closely adjacent to said sidewalls, the improvement which comprises auxiliary longitudinal grooves provided on the surface of said bottom plate in parallel with said sidewalls, said auxiliary longitudinal grooves being positioned between 1 and 10 cm. from said sidewalls.

2. The electrolytic cell according to claim 1 wherein said auxiliary grooves are spaced from 2 to 5 cm. from the surface of said sidewalls.

3. The electrolytic cell according to claim 1 wherein said auxiliary grooves have a depth of 1 to 5 mm.

4. The electrolytic cell according to claim 1 which further includes at least one longitudinal anode support mounted on said bottom plate in parallel with said sidewalls, and additional auxiliary grooves on both sides of said anode support, said auxiliary grooves being parallel to said support and spaced therefrom l to 10cm.

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2. The electrolytic cell according to claim 1 wherein said auxiliary grooves are spaced from 2 to 5 cm. from the surface of said sidewalls.
 3. The electrolytic cell according to claim 1 wherein said auxiliary grooves have a depth of 1 to 5 mm.
 4. The electrolytic cell according to claim 1 which further includes at least one longitudinal anode support mounted on said bottom plate in parallel with said sidewalls, and additional auxiliary grooves on both sides of said anode support, said auxiliary grooves being parallel to said support and spaced therefrom 1 to 10 cm. 